Does the background vary?

(2/16/94)

Yes. Significantly. See the 'Background' category in the
Data Analysis Frequently Asked Questions. All
components of the background, except for the particle background, vary
considerably. The cosmic background in both the hard and soft bands vary
by at least a factor of five over the sky. In addition, they vary
independently, resulting in a significant change in the spectral
distribution of the cosmic background. The non-cosmic background
components can have even greater variation. The intensity of scattered
solar X-rays can vary from zero for night-side observations to more than
50 counts/s for day-side observations early in the mission. Auroral
X-rays can produce count rates well over 200 counts/s but are in general
zero. Long-term enhancements, which mostly affect the 1/4 keV band, can
vary between zero and about five counts/s. In addition, the lowest few
channels are affected by afterpulses, which are time dependent.